Add a conditional control to mkfs_plugin to avoid using filesystem options...

Following up on Debian bug report #1108498, this patch adds a conditional control (target_old) to mkfs_plugin which, when activated, avoids using filesystem options that cause compatibility issues with older systems. This switch will disable the orphan_file, which prompted the bug in question, plus large_dir and metadata_csum_seed, introduced two years ago due to a very similar issue. Please note that I didn't test this MR so far.